How Do I Analyze a Radiograph of the Chest

First of all, it is important that you approach the CXR without fear—its analysis is not black magic. Secondly, you should always follow a rigid but commonsense sequence of image analysis in order to not miss an important finding. Why don't you stick to the following suggested scheme for now and try it out on a CXR without abnormal findings (Fig. 6.1a, b).

First Determine the Image Quality

Is the exposure dose adequate? Can I see the pulmonary vasculature behind the heart and underneath the diaphragmatic contour? (One-third of the lung and thus one-third of the pathological findings are situated in these dense areas.) Can I see the vessels in the central lung around the hilum well or are they too dark to evaluate?

Is the exposure time short enough? Is the heart contour really sharp? It is the fastest moving structure in the thorax (at a breathtaking top speed of 7km/4.3 miles per hour!).

Was the patient standing or lying? Do I see an air-fluid level in the stomach (Fig. 6.1c, Fig. 6.2a)? Do the scapulae project outside of the lung fields (Fig. 6.1, Fig. 6.2, standing patient)? Is the medial contour of the scapula projecting over the lungs? Is the mediastinum shortened in the vertical direction and widened (Fig. 6.3, lying patient)?

Is the patient correctly positioned? Are the spinous processes centered between the sternoclavicular joints (Fig. 6.1c)? Does the anterior end of the bony part of the first rib just about project over the level of the 4th thoracic vertebral body (Fig. 6.1c)?

Did the patient stand still and manage to hold the breath?

Are the rib contours and the diaphragmatic outline sharp? Not all patients understand the local language or can do what they have been asked to.

Now Go Ahead and Analyze the Thorax

With a quick glance we note name, age, and sex of the patient before we begin the actual analysis of the standard radiograph of the chest.

Table S.1 Suggestions for diagnostic modalities in chest imaging1

Clinical problem

Investigation

Comment

Nonspecific chest pain

CXR

Not indicated initially. Main purpose is reassurance.

Upper respiratory tract infection

CXR

Not indicated.

Chronic obstructive airways disease or asthma; follow-up

CXR

Only if signs or symptoms have changed, asthma is life-threatening, or treatment fails.

Pneumonia

CXR

Majority of patients with community-acquired pneumonia will show radiological resolution at 4 weeks. In smokers, the elderly, and chronic airways disease, resolution may be prolonged. If patients become completely asymptomatic, no follow-up CXR is needed.

Pneumonia, adults: follow-up

CXR

If patients become completely asymptomatic, no follow-up CXR is needed in younger patients or in the absence of a significant smoking history. If symptoms persist, in the elderly and smokers, 6 weeks follow-up is advised.

Acute chest infection, children

CXR

Not indicated routinely. Initial and follow-up films are indicated in the presence of persisting clinical signs or symptoms or in the severely ill child. Children may have pneumonia without clinical signs.

Investigation of choice; will show and exclude relevant pulmonary embolism as well as other differential diagnoses (e.g., aortic dissection); dedicated "one-stop shop" PE protocols will also demonstrate deep vein thrombosis from the knee up in the same procedure.

Investigation of choice; will show and exclude dissection as well as other diagnoses (e.g., pulmonary embolism).

CXR

Baseline investigation to exclude other causes; rarely diagnostic.

Intensive care patient

CXR

CXR is most helpful when there has been a change in symptoms or insertion or removal of a device. The value of the routine daily CXR is increasingly being questioned. CT is a useful adjunct for problemsolving in the critically ill.

Preemployment or screening medicals

CXR

Not indicated. Justified in a few high-risk categories (e.g., at risk immigrants with no recent CXR). Some have to be done for occupational (e.g., divers) or emigration purposes (UK category 2).

Preoperative

CXR

Not indicated routinely. Exceptions before cardiopulmonary surgery, likely admission to ITU, suspected malignancy or possible TB. Anesthesiologists may also request CXRs for dyspneic patients, those with known cardiac disease and the very elderly. Many patients with cardiorespiratory disease have a recent CXR available; a repeat CXR may not be necessary under these circumstances.

Cancer patients

Diagnosis

CXR P-A and lateral

But can be normal, particularly with central tumors. Marking of nipples may reduce number of fluoroscopies in tumor patients with suspected metastases.

CT

Many centers proceed directly to bronchoscopy, which allows biopsy. CT is superior in identifying lesions responsible for hemoptysis.

Fig. 6.1a This is a normal CXR of a female. Note the increased density of the lower lung due to the mammary glands. The contours of the breasts are not always visible as well as this. In a patient who has undergone mastectomy the operated side may be less radiopaque, resulting in a relative increase on the contralateral side! If one breast is missing, unintended rotation of the patient may ensue when the patient is asked to "hug" the detector or film cassette—how you control for that is outlined in c.

b Here you see a normal lateral view of a slim female. Once you identify left and right hemidiaphragms (silhouette sign of the heart, air in the colon and the stomach!), you can also assign the posterior costophrenic sulcus and the posterior lung margin to the proper side. Now find the aortic arch. Draw the pulmonary artery in your mind (see also Fig. 6.2a) c This is a normal CXR of a male. You can appreciate the handy "spirit level" all of us carry around—the gastric bubble. The medial contours of the scapula are visible outside of the lungs. There is no doubt: this radiograph was performed with the patient erect. The spinous processes of C7 and T1 are marked as posterior point of reference, the medial borders of the clavicles as anterior point of reference. This patient is well positioned!

First follow the diaphragmatic contour: Is it well demarcated and do the costophrenic sulci show a normal depth and pointed tip? Or is there an upward-curved line (as for instance in a pleural effusion)? The right lower lobe of the lung covers the entire surface of the right hemidiaphragm;

in the left hemithorax the heart abuts the hemidiaphragm anteriorly and the left lower lobe touches the remainder of it. If the lower lobe is not aerated, the hemidiaphragmatic contour is no longer perceptible and we lose its silhouette (this is the "silhouette sign," see p. 23-24).

I "Silhouette Sign"

Fig. 6.2a The silhouette sign helps us to assign the hemi-diaphragms to their correct side. The heart sits on the left hemi-diaphragm, which is why the anterior part of the hemidiaphrag-matic contour is not visible. Together with the gastric bubble, the splenic flexure of the colon is located underneath the left diaphragm. Got it all lined up? The arrow points to the right hemidiaphragm. Trace its contour back to the right posterior pleural margin and the right costophrenic sulcus. You can now assign pleural lesions such as pleural effusion to their proper side. The inverted comma is drawn for orientation—it corre-

Fig. 6.2a The silhouette sign helps us to assign the hemi-diaphragms to their correct side. The heart sits on the left hemi-diaphragm, which is why the anterior part of the hemidiaphrag-matic contour is not visible. Together with the gastric bubble, the splenic flexure of the colon is located underneath the left diaphragm. Got it all lined up? The arrow points to the right hemidiaphragm. Trace its contour back to the right posterior pleural margin and the right costophrenic sulcus. You can now assign pleural lesions such as pleural effusion to their proper side. The inverted comma is drawn for orientation—it corre-

Now trace the visible pleural border up to the lung apex:

Is the pleura smooth? Is it fitted tightly to the rib cage or not—as, for example, in pleural scarring, in pleural effusion in a recumbent patient, or in a patient with a pneumothorax?

sponds to the left pulmonary artery. Do you recognize the "black hole" that the comma bends around? The major and minor fissures are both easily identified on properly exposed radiographs and they provide clues for orientation in the process of allocating a lesion to a specific lobe. Note howfar superiorly the lower lobe extends!

b Now go ahead and use your fresh knowledge in the analysis of this image. Which heart valve is calcified in this patient?

Fig. 6.3 This CXR was performed with the patient in bed without a scatter-reducing grid—that is why the inherent image contrast is l ower. The mediastinum is compressed, the diaphragm is elevated owing to the increased abdominal pressure. The upper lobe pulmonary vessels are well filled because the hydrostatic pressure in the recumbent patient is similar in the upper lung to the pressure at the lung bases. The superior mediastinum is a little wider than usual in a bedside CXR. Do you need to worry? Have you checked the rotation of the patient?

Inspect the lung parenchyma: Is the radiographic density of the lungs homogeneous and symmetric? (Asymmetry may be caused, for example, by freely mobile pleural effusions causing a more radiopaque appearance of the affected side in a supine patient.) Are there increases and/

I Portable Chest Radiograph: Normal Findings or decreases in radiolucency (for example, regional overinflation, opacities)? Can circumscribed opacities be seen (nodules, consolidation)? Do the vessels appear to be sharp and of normal caliber, or are they fuzzy and prominent (as, for example, in pulmonary edema)? Do they branch in a harmonic fashion or like the branches of an old apple tree (as, for example, in emphysema)? Briefly check the position of the minor fissure, the thin pleural leaf that separates the upper and middle lobes on the right side (Fig. 6.1a).

Have a look at the superior mediastinum: Is it of normal width? Is the trachea in midline and of normal caliber? Or is the trachea displaced and narrowed (such as in a patient with a goiter)? Does the aortic arch show a normal configuration or is it widened (as can be the case in patients with aortic aneurysm or traumatic pseudo-aneurysm)? Is its lateral contour visible ("silhouette sign," see p. 23-24)? Is the outline of the trachea immediately adjacent to the aortic arch or is there a perceptible separation between these two structures (for example, as caused by enlarged lymph nodes)? Is the azygos vein of normal caliber (approx. 1 cm; Fig. 6.1c), or is it enlarged (as, for example, in superior vena cava obstruction or right heart dysfunction)? Are the tracheal bifurcation and carina normally configured (Fig. 6.1c)? Or do they appear elevated and widened (such as in an enlarged left atrium or enlarged infracarinal lymph nodes)?

Now let us review the hila: Is the left hilum about a finger's width higher than the right (due to the left pulmonary artery crossing over the left main stem bronchus)? Or is one of the hila displaced (for example, by loss of volume or scarring in the upper lobe on that side)? Is the aorto-pulmonary window—the angle between the aortic knob and the left pulmonary artery—empty? Are the hila bilaterally enlarged (for example, in pulmonary hypertension or bilateral lymph node enlargement) or is only one hilum of irregular shape (for example, due to a tumor)?

Look at the inferior mediastinum: Is the heart contour of normal size and configuration? The width of the heart may not exceed half the maximum diameter of the chest. Do you see additional shadows projecting over the heart (for example, pericardial calcifications in constrictive pericarditis, coronary or valvular calcifications, metal valve re-

| Checking the Ribs: Normal Findings_

placements, cardiac pacer or defibrillator electrodes)? Are the heart contours visible all around? The right heart contour is adjacent to the middle lobe, the left contour by the "lingula" of the upper lobe of the left lung (these are other potential sites for a "silhouette sign," see p. 23-24). If the lower left heart contour is rounded and extends far laterally, the left ventricle is enlarged (for example, in cardiac muscular hypertrophy due to arterial hypertension or aortic valve stenosis). If the concavity of the upper left heart contour turns convex, this may be due to pulmonary arterial enlargement in patients with valvular disease or sometimes in patients with severe pulmonary arterial hypertension.

Observe the heart shadow and the space underneath the diaphragmatic contour: About one-third of the lung is located in these areas; consequently, about one-third of the pathology also hides there. Try to trace the course of the vessels in the heart shadow and underneath the diaphragmatic domes! In perfect radiographs of perfect patients you can see the anterior and posterior margins of the costo-phrenic sulci.

Finish up and check the thoracic wall and soft tissues:

How wide is the soft tissue mantle of the thorax; how muscular, adipose, or edematous is the patient? Is there perhaps a breast missing or are there clips in the axilla in a patient with treated breast cancer? Now analyze the cervical region: Is there any air in the soft tissue (for example, in soft tissue emphysema due to trauma or a leaky chest tube); are the vocal cords visible at the upper end of the trachea (essential to determine the correct position of an endotracheal tube!)?

Finally have a look at the thoracic skeleton: A first glance goes to the shoulders and clavicles, the second scans the spine. Then rotate the radiograph by 90° to better appreciate the ribs without your attention being distracted by the heart and lung (Fig. 6.4). Experienced radiologists will applaud this procedure and give you additional points in your oral exam. Now trace every single rib from the spine to its ventral end. Pay attention to discontinuities and irregularities in the rib margins and to soft tissue shadows alongside the ribs: Are variants present such as bifid ribs or do you see fractures, metastases, or destructions due to tumors such as multiple myeloma?

Fig. 6.4 This is how you evaluate the thoracic skeleton best—clockwise or anticlockwise rotation (90°). Trace every single rib over its complete course. For specific bone problems, a dedicated rib series of the affected hemithorax with a different (lower) exposure voltage (approx. 80 kVp) is performed.

Now Get Additional Information from the Lateral Chest Radiograph

When looking at the lateral CXR, things only get more complicated: both lungs and hila are now superimposed. The first step is to become familiar with the appearance of normal anatomical structures so that you can recognize them on a lateral CXR like good old friends and notice when one is missing.

Begin with both hemidiaphragms: Which one is the left hemidiaphragm (see Fig. 6.2a)? Follow the contour of both hemidiaphragms anteriorly, starting at the bottom of the respective posterior costophrenic sulcus. Now trace the posterior pleural border toward the upper thorax. Localize both the minor and the major lobar fissures (by the way, which side was the minor fissure on?).

Analyze the hila at this time: The left pulmonary artery swings out of the pulmonary trunk up over the left main stem bronchus, assuming the configuration of an inverted comma. The left main stem bronchus is part of the "black hole" that you see on most films. On a normal CXR, essentially all visible dense structures within the lungs should show a typical vascular, branching course toward the hilum. If that is not the case, you need to explore further.

What do the heart contours tell you? The anterior heart contour corresponds to the anterior wall of the right ventricle and is seen behind the anterior thoracic wall, mainly made up of the sternum centrally, which is why this space is called the retrosternal space. If the right ventricular border reaches the mid and upper sternum, the ventricle is enlarged. The posterior heart contour on the lateral CXR corresponds to the left atrium in its upper part and to the left ventricle in its lower part. A small amount of barium swallowed by the patient prior to taking the CXR outlines the course of the esophagus and lets you better appreciate the outline of the atrium if this is of clinical importance.

Finally put everything else in order: The contour of the aortic arch is visible throughout most of its course. It runs in a wide arc over the hilum. Atherosclerosis of the aorta is easily appreciated on this projection. The "black hole" mentioned before can help us once more (see Fig. 6.2): If we draw a line from there to the anterior costo-phrenic sulcus, the aortic valve typically projects superior to the line, the mitral valve inferior to it. Pretty good trick, isn't it? Finally we take a good look at the upper retroster-nal space, which should be rather radiolucent because here both lungs meet anterior to the mediastinum. In emphysema this space could be widened; if there is a tumor or goiter present, the space becomes radiopaque.

I See an Abnormality—What Do I Do Now?

You proceed as systematically as you did during the image analysis described above. First of all the diagnostic thinking needs to be pointed in the right direction! If the abnormality concerns the lung parenchyma, the following questions need to be answered:

• Is it an opacity or an abnormal radiolucency?

• Is it a rather circumscribed or a diffuse process?

• Are we dealing with a solitary lesion or are multiple lesions present?

• Is the lesion homogeneous or heterogeneous?

• Does the diffuse process have a patchy (acinar) or fine linear (reticular) or diffusely nodular pattern of appearance?

If the abnormality is located in the mediastinum, it suffices to localize the lesion: hilar region, upper or lower, anterior or posterior mediastinum. If the lesion is in the thoracic wall, any involvement of the ribs needs to be determined.

Additional studies may help to show the lesion more clearly and in more detail; for example, a quick fluoro-scopy of a nodule in the central lung or an elevated hemi-diaphragm, or an apical lordotic view when dealing with an abnormality in the lung apices (Fig. 6.5). After that the diagnostic approach starts to vary. We will see and exercise this in the respective cases. Now you should be about ready to tackle the first clinical case.

I Hyperlordotic View

I Hyperlordotic View

Fig. 6.5a There is a small nodule seen above the right hilum (arrow). Is it a real finding?

b The apical lordotic view shows a normal superior lung (the patient leans back during the exposure and thus elevates the clavicles up over the lung apices). In retrospect the "nodule" must have been a prominent vessel viewed end-on or "down the barrel."

Fig. 6.5a There is a small nodule seen above the right hilum (arrow). Is it a real finding?

b The apical lordotic view shows a normal superior lung (the patient leans back during the exposure and thus elevates the clavicles up over the lung apices). In retrospect the "nodule" must have been a prominent vessel viewed end-on or "down the barrel."